1. Field of the Invention
The present invention relates to high frequency front-end modules and duplexers, and in particular, to a high frequency front-end module that processes a plurality of high frequency transmission and reception signals having different frequency bands and a duplexer for branching reception signals having different frequency bands.
2. Description of the Related Art
In a typical high frequency front-end module of a mobile communication device, such as a cellular phone, surges (electrostatic discharge (ESD): frequencies of approximately 300 MHz) enter through an antenna. Because of this, an anti-surge element is disposed between an antenna terminal and the ground in most cases. Japanese Unexamined Patent Application Publication No. 2003-18040 discloses disposing an inductance element between an antenna terminal and the ground, and Japanese Unexamined Patent Application Publication No. 2003-101434 discloses disposing a varistor between an antenna terminal and the ground. However, an anti-surge element directly attached to an antenna terminal has a fundamental problem of increasing loss of a transmission or reception signal.
For a high frequency front-end module that includes a diplexer for branching a signal of a relatively high pass band of that is equal to or greater than about 1.5 GHz (hereinafter referred to as a high frequency signal on a higher side) and a signal of a relatively low pass band that is equal to or less than about 1.0 GHz (hereinafter referred to as a high frequency signal on a lower side), a surge does not cause a major problem in a signal path for high frequency signals on a higher side because the surge is attenuated by a high-pass filter of the diplexer, whereas a surge may enter a signal path for high frequency signals on a lower side.
In particular, because an element that is sensitive to a surge, such as an acoustic wave filter, is typically disposed in a reception-signal output terminal on the lower side, components for protecting such an element against surges are necessary.